I had my A/C system replaced in March of 07 all ACDelco parts in a professional shop. about 2 months ago the A/C light came on in the info panel and the A/C would not engage. I took it back to the shop and he said his flashed the CPU becuase sometimes it locks up and causes the A/C to do that (or something to that effect) The shop is owned by a man my family and I have know for 30 years, I felt he's wasn't going to screw me, so I went with it. Anywho, the Data display panel will show a "C" from time to time (after the flashing) and stay that way for a few miles then back to normal with no data lost. The Fuel panel is not effected. I ran a diagnostic and only got F31. (on a side note the econ light on the display flashes in an erratic pattern during the test, never seen it do that before.) I was wondering if this could be the cause of the A/C not blowing cold anymore and cycling from cool to fan like every few minutes (it is set to high with window down to ensure the A/C contiunes to cool car.) Also heat is also acting the same way as well (warm then fan, etc.) Thanks for any help you can give.

Try pulling battery power for a few minutes and see if that helps.

Code F30 is set if the BCM is unable to receive data from the Electronic Climate Control (ECC) panel. Code F31 indicates that the same condition exists between the BCM and Fuel Data Center (FDC).

So does that mean the problem is in the ECC or the BCM? I added up all the times the Fuel Data Center goes "c". If there's any type of moisture in the air i.e rain, dew, etc. the display goes "c" like last night, except the display never returned to normal after driving a few miles. Also, the "c" now flickers a "d". I gonna check for lose connections on the BCM and CPU and see if that helps.